Unions frequently restructure through merger, most often in the form of absorptions involving one bigger union absorbing a smaller one. However, the individual-level effects of merger resulting in big amorphous organisations remain unclear. In this article, we highlight the role of the individual member in union absorptions, and investigate the relative importance of being a member of a large absorbing union or a small absorbed union, as well as the attitude of members towards merger in predicting post-merger member attachment. The results from longitudinal data before and after absorption showed that members’ attitude towards merger significantly predicted the members’ attachment levels after absorption—this was, however, not the case for union commitment. We also uncovered a significant interaction indicating that the effect of members’ attitude towards merger was more strongly related to perceptions of union support and instrumentality among members of the absorbed union.